Annulated pyridines like 9-amino-5,6,7,8tetrahydroacridine (tacrine) are drug or drug intermediates for various diseases like Alzheimer's disease, which is the most common cause of dementia in old people. Many methods of producing pyridine bases are known, for example reacting an aliphatic aldehyde and/or ketone with ammonia in gaseous phase using a solid acid catalyst such as amorphous aluminosilicate and the like (Japanese Patent Application Kokai (Laid-open) No.63176/76, Japanese Patent Publication No.3 41546/71 and 32790/69). Crystalline aluminosilicate, called zeolite is used as the catalyst for producing pyridine bases from an aliphatic aldehyde and ketone (or formaldehyde) and ammonia (U.S. Pat. No. 4,220,783, Japanese Patent Application Kokai (Laid-open) No.38362/85, Indian Patent Nos. IN-185390, IN-185654). According to these processes one ring pyridine compounds are produced but fused ring heterocyclics have not yet been reported over zeolite molecular sieve catalysts. Increasing applications of these annelated pyridines demand an eco-friendly, economical and free handling process. The present invention provides an eco-friendly and economical process for synthesis of a variety of these compounds.
The synthesis of octahydroacridine and octahydrophenanthridine was carried out using homogenous catalyst like ammonium acetate and ammonium hydroxide but the yield were lower than 54% and usual disadvantages of homogenous catalysis were observed (J. Org. Chem. 42 (No. 16), p 2742 (1977). The synthesis of octahydrophenanthridine was also carried out using p-tolune sulfonic acid and POCl3 as homogenous catalyst(s) from 2(1-cyclohexenyl)-cyclohexanone and RCONH2 (U.S. Pat. No. 4,006,236 (1977). The reaction time is longer, 10-24 hrs and the catalyst can not be reused and silica-alumina, chronia or magnesia catalyst(s) at comparatively high reaction temperature 180-425° C. in vapour phase with low selectivity for a particular product. Our process using molecular sieve is eco-friendly, catalyst is reusable, separation is easy and selective.